RecruitingDevice studyElectrophysiology of Fetal ArrhythmiaFetal research and clinical practice has been hampered by a lack of suitable investigational techniques. Currently, ultrasound is the only widely used method of studying fetal anatomy and physiology, but it has significant limitations for assessment of cardiac rhythm. The proposed study will allow the investigators to evaluate fetal magnetocardiography (fMCG) as a new tool for the study of normal and abnormal fetal heart rate and rhythm.